Purpose :
If there is one thing that needs to be tested for at a body of water, it is DO. DO, or dissolved oxygen, is what it sounds – how much oxygen is dissolved in the water. All (aquatic) organisms need oxygen to survive. It is important to test for DO because this is a factor that can in itself help determine the health of the pond. If the reading is high, we know that photosynthesizers are healthy and that the water can support large organisms, such as trout. If the DO reading is low, this could be an indicator that there is thermal pollution, excessive decay, sewage, or algal blooms, etc. Also, it is important to know that DO is temperature dependent; cold water can hold more dissolved oxygen than warm water.
Materials:
Only one piece of equipment needs to be brought from the classroom to the body of water, it is the DO probe. The probe is in a big black accer case. Inside there is the probe; it is a black control pad with several feet of thick yellow rubber cord connected to the thick tube that is the actual probe.
Field Test:
The DO test needs to be performed from the boat because DO needs to be measured from different depths. The first step is to go out into the boat with the DO probe; one person rows and the other uses the DO device.
Next, turn on the probe by pressing the black power button in the middle at the bottom of the control pad.
Measure DO at the surface first. Lower the bottom part of the probe so that it is just below the surface. Then, press the green “read” button on the right on the control pad. This tells the probe to begin testing. A small bar in the top left corner of the control pad’s screen will start to fill, like a loading bar on a computer. Once the bar is full, it means the test is complete; it is calibrated and has found the DO for this depth. The DO reading for this depth will appear in big numbers in the center of the pad. It is also very important to note the temperature of the depth, the temperature is found in the top right corner of the screen. Record the DO value in mg/l and the temperature in degrees Celsius.
Next, perform the same steps but instead of at the surface, lower the probe to the bottom. The steps are exactly the same. It is wise to get several DO readings at several different locations, each with two readings (at the surface and at the bottom).
After you have the DO readings from the surface and the bottom, you have completed DO testing and can return to the dock.
Once back at the dock, coil up the rubber yellow cord and put this, the probe, and the control pad back in the case.
Finally, tell the record keeper the results. Make sure that there are two separate readings, one for surface and one for bottom. Both surface and bottom should have a DO measurement in mg/l and a temperature reading in degrees Celsius.
Lab Test:
All of the DO data is obtained in the field, and no work needs to be done in the lab except for filling in the Q table. To fill in the Q table for your lab, you need to know the DO % saturation. To find this out you use the “level of oxygen saturation chart.” You need to know the temperature and the DO mg/l to figure this out. You connect the temperature reading and the DO reading on the chart, and where this line intercepts the slanted % saturation line; this is the DO % saturation reading. This means that the water holds this percentage of what it can hold in oxygen. This is the only lab component to the DO test.
Readings:
DO measurements can fluctuate, they can be between 4-10, but can also be lower or higher depending on the health of the pond. DO readings are higher in colder water bodies because cold water can hold more oxygen, (also large fish populations can live in cold water because of this). A low DO reading can indicate that there is pollution or a warm temperature in the water, and the opposite for a high DO reading. DO measurements tell us how much oxygen water holds and tells us how healthy the pond is. DO is the most important test because every organisms needs oxygen to survive and knowing the DO can help us to determine a water ecosystem’s health.
If there is one thing that needs to be tested for at a body of water, it is DO. DO, or dissolved oxygen, is what it sounds – how much oxygen is dissolved in the water. All (aquatic) organisms need oxygen to survive. It is important to test for DO because this is a factor that can in itself help determine the health of the pond. If the reading is high, we know that photosynthesizers are healthy and that the water can support large organisms, such as trout. If the DO reading is low, this could be an indicator that there is thermal pollution, excessive decay, sewage, or algal blooms, etc. Also, it is important to know that DO is temperature dependent; cold water can hold more dissolved oxygen than warm water.
Materials:
Only one piece of equipment needs to be brought from the classroom to the body of water, it is the DO probe. The probe is in a big black accer case. Inside there is the probe; it is a black control pad with several feet of thick yellow rubber cord connected to the thick tube that is the actual probe.
Field Test:
Lab Test:
All of the DO data is obtained in the field, and no work needs to be done in the lab except for filling in the Q table. To fill in the Q table for your lab, you need to know the DO % saturation. To find this out you use the “level of oxygen saturation chart.” You need to know the temperature and the DO mg/l to figure this out. You connect the temperature reading and the DO reading on the chart, and where this line intercepts the slanted % saturation line; this is the DO % saturation reading. This means that the water holds this percentage of what it can hold in oxygen. This is the only lab component to the DO test.
Readings:
DO measurements can fluctuate, they can be between 4-10, but can also be lower or higher depending on the health of the pond. DO readings are higher in colder water bodies because cold water can hold more oxygen, (also large fish populations can live in cold water because of this). A low DO reading can indicate that there is pollution or a warm temperature in the water, and the opposite for a high DO reading. DO measurements tell us how much oxygen water holds and tells us how healthy the pond is. DO is the most important test because every organisms needs oxygen to survive and knowing the DO can help us to determine a water ecosystem’s health.
Meg & Megan (P6)